Sullivan said Thursday morning that police are investigating the thefts and believe they could have been stolen by people hoping to sell them for scrap. He said public works employees noticed the covers, which weigh nearly 100 pounds, were missing from drains on Commercial, Hayward and Old Elm streets over the last two days.

Sullivan said he’s concerned someone could fall into an open storm drain, which average about 4 feet deep, if the thefts continue.

“You could have a small animal, you could have a child, you could have someone running along and catch their leg and fall in,” said Sullivan, who added that he’s particularly concerned about bicyclists and motorcycle riders.

The storm drain covers are rectangular and typically found along the side of roads near the curb. Because of their weight, Sullivan said police believe the thefts are the work of more than one person, probably working during the night.

The mayor is asking anyone who sees an uncovered storm drain to contact the Braintree Department of Public Works immediately at 781-794-8950.